In a bending machine of this kind, an angle iron is detained by two couples of lower coaxial rollers through the one flange thereof clamped between said coaxial rollers and the other flange facing outwardly. When an angle iron is so positioned, it is called “external-flange” angle iron. While the angle iron is so clamped, it is worked by deformation by means of said lower rollers and a third roller travelling transversally toward the angle iron.
A working operation of this kind usually involves the generation of a twisting moment tending to modify the normal orthogonality of the flanges of the angle iron, causing a unacceptable deformation of twisting, that compromises the result of the working operation.
There are known prior art documents that disclose an anti-twisting action.
In U.S. Pat. No. 2,365,882 A (Kane & Roach Inc.), that doesn't relate to an “external-flange” angle iron, one flange of the angle iron is clamped by the upper roller, and the other flange thereof faces inwards.
GB 715 897 A (Leycure) discloses a bending machine, in which the angle iron being worked is positioned with both the flanges thereof being clamped among the upper roller and the lower rollers. A plate, which is coaxial to the upper roller, serves only the function to retain the angle iron against the upper roller and near the axis thereof, but doesn't allow for the twisting of the one flange of the angle iron to be prevented.
In a bending machine disclosed in CH 301 505 A (Kausler-Hutter), an angle iron being worked is not positioned with one flange thereof being clamped by said lower rollers, and the other flange facing outward. Further, the antitwisting action is performed on the internal flange of the angle iron, and not on the external flange.